Stars come in huge range of different sizes. Neutron stars can be just 20 to 40 km in diameter, whereas white dwarf can be very similar in size to Earth's. The largest supergiants, on the other hand, can be more than 1500 times larger than our Sun. With the Sun having a diameter of 695,000 km, this means that in the extreme cases, we are looking at a star of over 1,000,000,000 km.